Hopper washing



March 23, 1954 4 SheetsSheet 2 l -5| 52 f 53 -l INVENTORS Er:

ALEXANDER N- CROWDER ATTORNEYS March 23, 1954 s. RABKIN ET AL HOPPERWASHING Filed Dec. 5, 1950 4 Sheets-Sheet 3 loo INVENTORS.

-SAMUEL RABKIN 8. ALEXANDER N. CROWDER BY jwwdwm ATTORNEYS March 23,1954 s RABKlN ET AL 2,672,946

HOPPER WASHING Filed Dec. 5, 1950 4 Sheets-Sheet 4 us we I07 "0 SAMUELRABKIN 8. ALEXANDER N. CROWDER ATTOR N E Y5 Patented Mar. 23, 1954Samuel Rabkin,

Union, and Alexander Crowder, Bound Brook, N.;.L, assignorsto ResearchCorporation, New York, N. Y.,' a corporation of New YorkApplicationDecember 5, 19511,,Serial No..199,184

.7 Claimfi,

I This invention relates to the washing of hoppers of electricalprecipitators, especially the hop-- pers-of ,precipitators employed tocollectash from the gasesresultingfrom the burning of black liquor inthesulfate paper making process. The invention is particularly concernedwith apparains r pp y n a d apply g W s in liqu d to; theinteriorsurfaces of the hoppers to maintain them in a clean condition and'to'flush out collectedlmaterial.

Anobject of the invention is tov P d HDD ratus for washing or flushingthe hoppers of electrical precipitators -efiectivel y,. simply andeconomically.

Ano.ther-object:o.f the, invention-is to provide ai-honper washingSystem wherein the washing liquid -not only-Jflushes the interiorsurfacesof the -.hopper but also flushes those parts of the washingsystem that are exposed to .dust fall within the hopperand thus areprone to collect dcn itsc precipitated material.

Another object is to provide in such a wash ing systema sealing .devicewhereby flushingliquidand collected material :is removed from the hppers without escapeof gas through the liquid outlet.

Still another object is to provide av hopper washingsystemfor electricalprecipitators that greatly improves thecollection and disposition .ofwater soluble precipitated material such as ashborne in gases fromrecovery furnaces in which black liquor is burned.

These and other objects of the invention, asmayappear hereinafter, arerealizedin-an electrical-prcc pitator having theusual casing, com,plementary high tensionand extended surface electrodes in the casing,andzgas inlet and gas, outlet means in the casing directing a streamofgas to be-cleaned between the electrodes, a hopper in thebottom of thecasing receiving'precipitated material removed from the electrodes anddischarge means in the hopper, washing means'for the hopperincludingailiquid conduit extending substantially along an upper edgeof the,hopper, the conduit having liquid :outlet means positioned to dischargewashing liquid against "anupper interior surface of the hopper, andmeans supplying washing liquidto the con.- duit.

The '{liquid conduit and liquid outlet means there'for may take avariety of forms. For exr ample, the liquid conduit may be an open toptrough, the lips of which form liquid outlet means spilling washingliquid over the .outside of the trough and overthe hopper surfaces. tobe washed.

2 Or, the liquid conduit may be a pipe extending around the top of theinside of the hopper and having holes or nozzles directing sprays ofwash? ing liquid over the surfaces to be cleaned.

The sealing device of the invention includesa discharge conduitleadingfrom the hopper'of the precipitator to a tank through which liquid flowsby gravity. The discharge conduit terminates .in the tank below thenormal level of liquid therein whereby escape of gas from theprecipitator through the hopper and the discharge conduit is prevented.

These and other features of the invention will bedes cribed withparticularity-in the following detailed description of severalembodiments as shown in the drawings in which:

Fig. 1 is a diagrammatic illustration of a black liquor recovery systememploying an electrical ip tatcr and Was i g ys m i ac rdance with theinvention;

Fig. 2 is an enlarged, vertical, partial sectional view of an electricalprecipitator and hopper washing apparatus suitable for use in the systemo Fig. 1;

Fig. .3 is a partial vertical sectional View of.an-. other ,precipitatoraccording to the invention;

Fig. 4 is a view similar to Fig. 3 of another form of the invention;

Fig, 5 is a vertical sectional view through the lower portion of stillanother form of precipitatcr; and

Fig, 6 is a sectional view taken along the line 6- 6 of Fig, 5,. y

The invention will be described by way of example with reference to a,black liquor recovery system forming an important part of a sulfateprocess paper mill. Such a recovery system is shown in Fig. 1 in which aweak black liquor storage tank It receives weak black liquor through thepipe II .from the pulp digesters (not shown) after the usual filtrationoperation. The weakblack liquor is an aqueous solution containing about15% solids, a large part of the solids content being organic in nature,including sodium sulfate. In the recovery system, the weak black liquoris concentrated to a solids content of about 58% and burned in a furnaceto oxidize and drive ofi most of the organic material, to evaporate thewater and to reduce the sodium sulfateto sodium sulfide which ispurified and reusedin the Pulp digesters.

Initial concentration of the weak black liquor is done in a multipleeffect evaporator 2 to which the .weakblackliquor .flows through a pipe13 acres is under control of a valve I4. The evaporator I2 is ofwell-known design and has a steam line l5 supplying steam to thecalandria of the last effect and a condenser, such as the barometriccondenser I6, receiving vapors from the first effect. The weak blackliquor flows through the efiects from right to left, as seen in Fig. 1,in countercurrent relation to the vapor flow, the latter being indicatedby the arrows at the top of the effects. Preliminarily concentratedblack liquor issues from the last efiect of the evapator l2 into theline I! and is forced by the pump l8 through pipes I9, 20, 2| and 22 toa conventional disc evaporator 23. Valve 24 in the line 2! controls theflow of black liquor to the disc evaporator.

In the disc evaporator, the preliminarily concentrated black liquor isconcentrated to a further extent by evaporation of water and the heavyblack liquor so produced flows through the pipe 24a to the heavy blackliquor storage tank 25.

Heavy black liquor from the tank 25 is forced by a pump 25 through thepipe 21 to a recovery furnace charging tank 23 from which it flowsthrough the pipe 25 to a furnace charger 3!] that delivers thecombustible heavy black liquor to the recovery furnace 3|.

The black liquor is burned in the furnace 31 to ash consisting chieflyof sodium sulfide and sodium carbonate, which ash is discharged from thefurnace into a dissolving tank 32 wherein it is dissolved in water andfrom which it is forced by a pump 33 to a point of disposition. Afterpurification, the solution of sodium sulfide is reused in the pulpmaking process.

Furnace gases that contain a heavy burden of moisture and notinconsiderable amounts of sodium sulfate and. sodium carbonate insuspension are passed at high temperature through a waste heat boiler 34in the furnace 3! where some of the sensible heat is recovered. Thepartially cooled furnace gases then are passed through the discevaporator 23 where some of the additional heat thereof is utilized toevaporatively concentrate black liquor flowing from the multiple effectevaporator [2 to the storage tank 25.

A fan 35 blows the furnace gases through an electrical precipitator 36and thence through the exhaust duct 31 to atmosphere. In theprecipitator, the furnace gases are substantially cleaned of their ashcontent, as will be explained in detail hereinafter, and theprecipitated ash is returned to the process.

Referring to Fig. 2, the precipitator 36 is shown in enlarged detailtogether with certain components of the washing system. Gas flowsthrough the precipitator from left to right in the direction of thearrows, entering the precipitator through the duct 38 and leavingthrough the duct 31. Within the precipitator there are extended surfacecollecting electrodes 39 and complementary discharge electrodes 40 inthe form of fine wires insulatedly suspended in parallel relation to thecollecting electrodes. The discharge electrodes are supplied with highvoltage current, usually direct current, by means of a high tensioncable M to which the wire electrodes are conventionally connected. Thusa high electric potential is maintained between the fine wire electrodes40 and the collecting electrodes 39 whereby corona discharge occurs atthe fine wire electrodes. The gas to be cleaned of ash passes betweenthe curtains of discharge electrodes and the collecting plates and inthese 4 zones the suspended particles become charged and are attractedto and deposited upon the collecting electrodes. Precipitated ash isremoved from the electrodes by any suitable electrode cleaning device,such as a rapper (not shown).

Beneath and communicating with the precipitating zone is a plurality ofhoppers 42 and 43 into which falls the ash dislodged from theelectrodes. This ash, as has been indicated, is soluble in water orblack liquor. It is removed from the hopper by hopper washing devices,three forms of which are shown by way of illustration in Fig. 2.

As seen in Fig. 2, the hoppers 42 and 43 have outlet openings 44 and 45communicating with a discharge header 43 conveying discharged materialto a tank 47. The tank receives preliminarily concentrated black liquorfrom the evaporators I2 through a pipe 48 under control of automaticvalve 43 and a manually controlled valve 50 shown in Fig. 1.

The tank has an agitator 5i, driven by conventional means (not shown)and a heating coil 52. An outlet pipe 53 conducts liquid from the tankto a pump 54 that forces liquid through the line 55 to the hopperwashing devices.

One such hopper washing device is shown in the hopper 43. It has troughs56 supported on brackets 51 carried by the precipitator casingstructure. Leveling screws 58 are threaded in the brackets, bear on thebottoms of the troughs, and are adjusted to level the troughs. The edgesof the troughs that run parallel to the sides of the hopper are bentdownwardly to provide overflow lips 59. Lying along or close to thebottoms of the troughs 55 are header pipes 60 connected at one end withwashing liquid supply pipe 55 and being capped at the other end. Theheader pipes have spaced holes through which washing liquid isintroduced into the troughs.

In operation, the troughs fill with washing liquid which flows over theedges of the troughs, down the lip portions 59 and is spilled upon thesides of the hopper. The liquid flows down the walls of the hopperwashing them free from precipitated material that has fallen thereon,and the washings are returned to the tank 41 through the pipe 46.

It is seen that the flushing liquid washes not only the sides of thehopper but also the lips and sides of the troughs. The tops of thetroughs present a horizontal free liquid surface. Thus it is evidentthat substantially all of the surfaces upon which falling precipitatedmaterial can impinge are subjected to the action of washing liquid.

If, as in the exemplary case, the precipitated material is soluble inthe washing liquid, such liquid becomes more concentrated in solute aswashing progresses and the concentration of solute in the tank 4? isalso progressively increased. When the concentration of the solution inthe tank reaches a desired value, some of the solution is drawn of!through the outlet pipe 6! to a pump 62 that forces it through a pipe 63to the disc evaporator 23, as seen in Fig. 1.

The level of the liquid in the tank t? is maintained constant by theautomatic admission of fresh liquor through the inlet pipe 43. Suchadmission of liquor is controlled by a liquid level sensitive device 64in the tank actuating a control motor 55 that operates a valve actuatingmotor 65 through the usual connection 5'! to admit treahfiliquorrras.i'equiredrandiltd.istop Ftheiinfiux orlfresh diquorwhenathesdesiredlevelin the tank' is attained. i

As best seeniinfi li'g. .2,Ythe':hopper discharge headenflfi has a.downturned leg 68 extending into the pool of liquid in the tank 4! anddischarging therein at the open end 6 9=locatedsubstantiallyrbeneathitheisurface ofiatheliquid pool. Theprecipitator 36 operates at superatmospheric pressures of from afractionofpninch-to a few ihchesiofjwater and'the'subinerged outlet ofthe dischargeheader provides a liquid seal wherebyfs'uch operating'pressurelisTmaintained while permitting outflow of washings' fromtheihop- IOthe'r' .iforms' of' hopper washing devices are shownin'thehopper '42 sting. 2. One form comprises a horizontal-pipe 10 extendingover the side qof athe hopper to bewashed. This pipe is onnectedwith :a.source. of washing liquidiunder pressure through the pipe H. Thehorizontal pipe 10 has a plurality of longitudinally spaced holesproviding jets directing sprays 12 of washing liquid upwardly a shortdistance into the air. At least a substantial part of the upwardlyprojected spray falls back upon the pipe HI thereby flushing the outsideof the pipe as well as the hopper surface.

Another form of flushing device is also shown in the hop-per 42 of Fig.2. This form has a trough I3, similar to the trough 56 describedhereinbefore, supported on brackets '14 on the precipitator casingstructure. The side wall 15 of the trough that is adjacent the wall ofthe precipitator or hopper is higher than the side wall 16 that facesthe center of the hopper. Liquid fed to the trough from the header 1'!thus flows over the top of the Wall 16 only. An apron 18 having ahook-shaped upper portion 19 is engaged over the top edge of the troughwall 16 and hangs downwardly substantially into engagement with an innersurface of the hopper 42. This apron extends for substantially the fulllength ofothe trough wall 16 and provides a surface down which thewashing liquid flows and from which the liquid is distributed to thehopper surface.

From a consideration of Fig. 1, it is seen that sulfate ash recovered inthe precipitator 36 is returned to the system in solution in blackliquor. This recovered ash is carried to the furnace 3| and againreduced to sulfide form.

It will be understood that the black liquor employed for washing theprecipitator hoppers may be drawn not only from the evaporators l2 butalso from any other convenient source. such as the weak black liquorstorage tank In, from the disc evaporator 23 or from the heavy blackliquor storage tank 25. A mixture of black liquors from these sourcesalso may be used as make up liquor for the hopper washing tank 41. Also,black liquor discharged from the washing tank 4'! may be conveyeddirectly to the recovery furnace 3| or to the heavy black liquor storagetank 25 instead of being conducted to the disc evaporator 23.

A somewhat modified form of hopper washing system is shown in Fig. 3.Referring to this figure, the precipitator hopper 80 has walls 8| and 82that slope at a small angle towards the center where there is located adrain pipe 83 emptying into a mixing tank 84 having an agitator 85.Washing liquid is circulated to spray pipes 86 and 8'! that extend along-the hopper walls 8| and 82 through the pipe 88, the pump 89 and iii) '6pipes 'fiu winds!) l; .ithe, i latter ibeinguncler-= control ofvaaval-ve 9.2.. Spray-pipes Stand-8'1 are provided with. spaced ho1es;93that, direct jets of iwashing liquid against the sides ioftheprecipitator and down over the hopper surfaces Bl-and. 82. A branch pipe'94 under control of a valve 954s used lto bleed-ofiffortified liquor.Makeup liquor is supplied-imequal volume to theonixing tank' iil'through 'apipemi. I i The washing system shown in Fig. 4 is simila'r tothat shown in 3. It-differs essentially from-thesys'tem of Fig. -3 :inthat' the liquid level in the mixing-tank 91 is automatically ma ntained at a predetermined level by means- Off a control system includinga level sensing device 98 in *the tank controlling a valve 9-9 inthemake upliquid' supply pipe 100. "The sensing-device operates throughconventional motors lliland "12 to admit iliquid ithrough valve 99 asneeded tozrestoreiliquidilevel:inithe tank. .J'

In Figs. 5 and 6, still another form of hopper arrangement and washingdevice is shown. The lower portion of the precipitator IE3 is dividedinto two similar hoppers H14 and I05 by a vertical wall 306. The bottomsID! of the hoppers have substantially plane surfaces sloping downwardlyfrom one side I08 to the other side 39. At the lower ends of the hoppersurfaces I01 are located transverse troughs H0, the bottoms of whichslope towards drain pipes l l I. At the upper ends of the slopingsurfaces I07 there are positioned transverse header pipes H2 havingnozzles H3 positioned to direct jets of washing liquid down and over thebottoms of the hoppers. Washing liquid is supplied to the headersthrough pipes 4.

In the washing system of Figs. 5 and 6, a copious flow of washing liquidis maintained over the surfaces I01 of the hoppers whereby they aremaintained in clean condition.

We claim:

1. In an electrical precipitator including a casing, complementarydischarge and extended surface dry electrodes in said casing and gasinlet and gas outlet means in said casing directing a stream of gas tobe cleaned between said electrodes, a hopper spaced from said electrodesin the bottom of said casing receiving precipitated material removedfrom said electrodes, and discharge means in said hopper, washing meansfor said hopper comprising a liquid conduit extending substantiallyalong the top edge of said hopper, said conduit having liquid outletmeans positioned to discharge washing liquid against an upper interiorsurface of said hopper, and means supplying washing liquid to saidconduit.

2. In an electrical precipitator includinga casing, complementarydischarge and extended surface dry electrodes in said casing and gasinlet and gas outlet means in said casing directing a stream of gas tobe cleaned between said electrodes, a hopper spaced from said electrodesin the bottom of said casing receiving precipitated material removedfrom said electrodes, and discharge means in said hopper, washing meansfor said hopper comprising a liquid conduit extending substantiallyalong the top edge of said hopper, said conduit having liquid outletmeans positioned to discharge washing liquid over said conduit andagainst an upper interior surface of said hopper, and means supplyingwashing liquid to said conduit.

3. An electrical precipitator as defined in claim 2 wherein said liquidconduit comprises a horizontal trough open at the top and said liquidoutlet means is provided by a lip of said trough.

4. An electrical precipitator as defined in claim 3 wherein said troughhas lips on opposite sides thereof positioned at the same level.

5. An electrical precipitator as defined in claim 2 wherein said liquidconduit comprises a horizontal trough open at the top thereof and havingan overflow lip along one side, and apron means extending from saidoverflow lip into substantial contact with a wall of said hopper.

6. An electrical precipitator as defined in claim 2 wherein said liquidconduit comprises a pipe and said liquid outlet means comprises spacedholes located in the upper portion of said pipe.

7. An electrical precipitator as defined in claim 1 wherein said hopperhas not more than two interior walls having substantial horizontal areacomponents, each of said walls sloping downwardly towards said hopperdischarge means,

8 said liquid conduit comprises a pipe, and said liquid outlet meanscomprises nozzle means spaced along said conduit.

SAMUEL RABKIN. ALEXANDER N. CROWDER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 768,450 Hardie Aug. 23, 1904 1,103,995 Murray July 21, 19141,250,088 Burns Dec. 11, 1917 2,031,437 Vincent Feb. 18, 1936 2,083,468Nahigyan June 8, 1937 2,095,597 Drylie Oct. 12, 1937 2,217,345 McGrawOct. 8, 1940 FOREIGN PATENTS Number Country Date 266,466 Italy July 29,1929

